Electronic structure of the SiP⁺radical on the basis ofab initioMRD-CI calculations

Ab initio MRD-CI calculations are reported for the potential curves of ground and excited states of the SiP+ molecular ion employing a large DZP AO basis. Secular equations of up to order 12 000 have been solved thereby and polarization functions of both d- and f-type have been included in the theoretical treatment. The ground state of this as yet unobserved system is found to be 3Σ-, in contrast to isovalent first row species such as CN+ and C2, which possess 1Σ+ ground and very low-lying 3Π excited states. The ordering of states in SiP+ is similar to that of Si2, but the energy separation between the X 3Σ- and A 3Π states is larger in the heteronuclear molecule. Spectroscopic parameters are also computed, including Franck-Condon factors and transition probabilities for various dipole-allowed excitations, in order to aid in the future experimental identification of this system. Finally a comparison of the electronic structure and properties of SiP+ is made with those of a series of isovalent systems for which calculation are available at the same level of theoretical treatment and the trends found thereby are analysed and discussed.